Thermally controlled switch



A. MORO July 4, 1967 THERMALLY CONTROLLED SWITCH Filed May 17, 1965 11:12:; VLF/271,14 .1, s

Inventor r4A 70N/0 M0190 y Jmr/M A tlorney United States Patent 3,329,788 THERMALLY CONTROLLED SWITCH Antonio Moro, Milan, Italy, assignor to Soc. per Azioni Fratelli Borletti, Milan, Italy, a company of Italy Filed May 17, 1965, Ser. No. 456,076 Claims priority, application Italy, May 15, 1964, 10,705/ 64 4 Claims. (Cl. 200-138) There are known devices called for brevity thermal switches, which are constituted substantially by a metallic housing in which are disposed a bimetallic plate and an electrical contact element, sealed into the housing. The contact element is fixed via a conducting pin to an external terminal to which is connected the end of a circuit that leads to the supply battery and which includes the acoustic and/or luminous signalling assembly. The housing, on the other hand, is fixed on the metallic body the attainment of the temperature limit of which is to be signalled, and has a part adapted to be immersed in the fluid (e.g. engine oil, radiator water or the like) the temperature of which is to be controlled.

The bimetallic plate is concave, and below a certain temperature value it remains concave towards the contact element. When the temperature reaches a predeter mined value related to the operating characteristics of the engine the plate snaps, reversing its concavity, and comes into contact with the said contact element, thereby closing the electrical circuit which then provides the required signal.

Devices of the above mentioned type have some disadvantages, howevenlt has in fact been found that the direct contact between the surface of the bimetallic plate and the contact element connected to the terminal is not always certain, either because the surface of the bimetallic plate is generally protected by a poorly conducting oily substance or because during storage and assembly it undergoes superficial oxidation which increases resistance to the passage of the electric current and hence reduces the certainty of the signalling operations.

It is of course possible to effect a treatment of the surface of the bimetallic plate so as to make it suitable for functioning also as an electric contact, However, the results obtained are not perfect, whilst the costs of the production are disproportionately increased.

The object of the present invention is wholly to eliminate these disadvantages. The invention relates, in fact, to a device having a bimetallic plate, characterised in that between the bimetallic plate and the contact element is interposed a flexible metallic element of good electrical conductivity, which alone has the function of closing the electrical signalling circuit. In this way the bimetallic plate no longer functions as a conducting element for closing the electrical circuit, but solely as a mechanical element for actuating an intermediate conducting element for closing the circuit.

The electrical operation of the thermal switch is thus independent of the conductivity of the bimetallic plate.

Some embodiments of the invention will now be described by way of example with reference to the accompanying drawing, in which:

FIG. 1 illustrates a thermal switch of known type in which the bimetallic plate closes the electrical circuit directly,

FIGS. 2 and 3 are diagrammatic axial sections of a 3,329,788 Patented July 4, 1967 thermal switch in accordance with the invention, with the parts in positions corresponding to the open and closed circuit respectively,

FIG. 4 is a plan view of the element for closing the circuit, interposed between the contact element and the bimetallic plate, and

FIGS. 5 and 6 illustrate two other possible forms of the device according to the invention.

The bimetallic plate 1 is disposed in the seating 2 of the body of the housing 3, When the temperature is low the position of the bimetallic plate is as shown in FIG. 2.

Above the bimetallic plate 1, against a circular shoulder 4, is clamped a resilient plate 5 which is preferably of the form shown in FIG. .4, viz. a ring 6 with a radial projection 7 extending inwardly and at a suitable distance beyond the centre of the ring.

The projection 7 is bent downwards slightly towards the bimetallic plate, as shown in FIG. 2.

The ring 6 of the plate 5 is pressed against the circular seating 4 by the ring 8, being locked by the insulating cap 9 which in turn is held in position by the rim 10 of the body 3. The electrical contact between plate 5 and housing 3 is thus fully ensured.

On the insulating cap 9 is mounted a pin 11 terminating at its lower end in a contact element 12, the external upper end being riveted to a terminal plate 13 or having any other known type of terminal connection, and being connected to the signalling circuit.

When the bimetallic plate reaches a predetermined temperature value it snaps upwardly and comes into the position 14. This snapping action brings the projection 7 into contact with the element 12, thereby closing the circuit from the terminal 13 to the body 3 and hence via the body of the vehicle to the battery.

The connection to ground is established by a screw plug 15 or by a flanged attachment 16 which connects the housing 3 directly to the surface of the body the temperature of which is to be measured.

In this way the bimetallic plate 1 no longer directly establishes the closing of the circuit, this being effected by the plate 7 which is made from resilient material of good electrical conductivity.

FIG. 5 shows a modification in which the bimetallic plate has an aperture at 17, and in the aperture is inserted a small contact element 17' associated with a resilient diametrical strip 18.

The circuit is thus closed by the strip 18 via the contact element 17' and the bimetallic plate functions solely as a mechanical control member.

Another embodiment is shown in FIG. 6, in which there is only a contact element 19 fixed to the centre of the bimetallic plate. In this case it is necessary to ensure good contact between the element 19 and a previously polished limited surface of the bimetallic plate.

The circuit is closed by the element 19 via the bimetallic plate, which is connected to ground via the supporting ring 2.

What I claim is:

1, A thermal switch comprising a metallic housing having a circular seating shoulder recessed therein, an insulating cap, a fixed metallic contact carried by the insulating cap and projecting into the housing, a bimetallic plate, and an electrically conductive resilient plate in the form of a.ring having a radially inwardly directed projection thereon, said ring being clamped between said shoulder and said insulating cap with said radial projection in front of said fixed contact, said bimetallic plate having two positions at ditferent temperatures, in one of which it presses said radial projection against said fixed contact thereby to close an electric circuit, and in the other of which it releases said radial projection from against said fixed contact, said projection being spaced from said fixed contact in said other position of the bimetallic plate.

2. A thermal switch as claimed in claim 1, said radial projection having an end portion inclined away from said contact and toward said bimetallic plate.

3. A thermal switch as claimed in claim 1, and a second circular shoulder recessed in the metallic housing and having a diameter smaller than the diameter of said first-named circular shoulder, said second circular shoulder being disposed on the side of said contact opposite said resilient plate, said bimetallic plate bearing against said second shoulder.

4. A thermal switch as claimed in claim 1, said fixed contact lying on the axis of said circular shoulder.

References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner.

H. GILSON, Assistant Examiner. 

1. A THERMAL SWITCH COMPRISING A METALLIC HOUSING HAVING A CIRCULAR SEATING SHOULDER RECESSED THEREIN, AN INSULATING CAP, A FIXED METALLIC CONTACT CARRIED BY THE INSULATING CAP AND PROJECTING INTO THE HOUSING, A BIMETALLIC PLATE, AND AN ELECTRICALLY CONDUCTIVE RESILIENT PLATE IN THE FORM OF A RING HAVING A RADIALLY INWARDLY DIRECTED PROJECTION THEREON, SAID RING BEING CLAMPED BETWEEN SAID SHOULDER AND SAID INSULATING CAP WITH SAID RADIAL PROJECTION IN FRONT OF SAID FIXED CONTACT, SAID BIMETALLIC PLATE HAVING TWO POSITIONS AT DIFFERENT TEMPERATURES, IN ONE OF WHICH IS PRESSED SAID RADIAL PROJECTION AGAINST SAID FIXED CONTACT THEREBY TO CLOSE AN ELECTRIC CIRCUIT, AN IN THE OTHER OF WHICH IT RELEASES SAID RADIAL PROJECTION FROM AGAINST SAID FIXED CONTACT, SAID PROJECTION BEING SPACED FROM SAID FIXED CONTACT IN SAID OTHER POSITION OF THE BIMETALLIC PLATE. 